Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer shaped semiconductor substrate, or "wafer". The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide, such as silicon dioxide, is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist. Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds, such as diazonaphthaquinones, that undergo a chemical change upon exposure to radiant energy, such as visible and ultraviolet light resulting in an irradiated material having differing solvation characteristics with respect to various solvents than the nonirradiated material. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers. After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated by placing a radiation opaque mask containing a transparent portion defining the pattern for the next circuit layer over the photoresist layer and then exposing the photoresist layer to radiation. The photoresist layer is then exposed to a solvent, known as developer, in which either the irradiated or the nonirradiated photoresist is soluble, which removes the photoresist in the pattern defined by the mask, selectively exposing portions of the oxide insulating layer. The exposed portions of the insulating layer are then selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. It is important that the remaining photoresist be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer. Following the etching process, the next circuit is deposited and the remaining photoresist is stripped from the surface of the wafer typically through the use of a solvent.
Photoresist and developer materials are typically applied to the wafer using a spin coating technique in which the photoresist is sprayed on the surface of the wafer as the wafer is spun on a rotating chuck. The spinning of the wafer distributes the photoresist over the surface of the material and exerts a shearing force that separates the excess photoresist from the wafer thereby providing a thin layer of photoresist on the surface of the wafer. It is necessary to produce a highly uniform photoresist layer to enable the subsequent circuit layers to be precisely placed on the wafer; however, a number of process conditions, such as photoresist temperature, system temperature, photoresist dispensing velocity, rotational speed, system air flow and solvent evaporation rate, greatly affect the characteristics the photoresist layer.
Many of the prior art attempts to provide a dispense system that produces a more uniform photoresist or developer coating have generally focussed on only a limited number of the aforementioned conditions. For instance, U.S. Pat. No. 5,427,820 issued to Biche discloses an photoresist dispense line which incorporates an annular flow path, surrounding an internal photoresist dispense line, in which a heat transfer medium is circulated to control the temperature of the photoresist and related U.S. Pat. No. 5,289,222 issued to Hurtig discloses a method for controlling the solvent evaporation rate in the spin coating apparatus. Also, U.S. Pat. No. 5,405,813 issued to Rodrigues discloses a method to distribute photoresist on the wafer by varying the rotational speed of the wafer during the dispensing and drying process. U.S. Pat. No. 5,020,200 issued to Mimasaka and U.S. Pat. No. 5,429,912 issued to Neoh disclose nozzle designs directed toward decreasing the force with which the photoresist or developer contacts the wafer surface by redirecting the flow of photoresist prior to contacting the surface of the wafer.
The prior art apparatuses and methods have only provided limited insight as to solutions to the problem of a nonuniform air flow field caused by the presence of the dispense line above the spinning wafer. The Biche patent notes that prior art heat transfer disperse devices are sufficiently large so as to block air flow which leads to non-uniform coatings (col. 2, lines 34-38) and suggests that the dispense line of the Biche patent was sufficiently small so that minimal interference to air flow occurs which results in uniform coatings (col. 6, lines 28-31). However, the presence of the dispense line remains an obstruction that causes nonuniformities in the air flow near the wafer.
The present invention is directed to apparatuses and methods for which overcome, among others, the above-discussed problems so as to provide a flow field having increased uniformity over the prior art resulting in more uniform coating being formed on the wafer and an apparatus that is easily maintained during operations.